What types of soils can be utilized in Modified Proctor tests?

The Modified Proctor test is specifically designed to evaluate the compaction characteristics of soils and determine their optimum moisture content and maximum dry density. This test is most applicable to soils that have a certain gradation, which is why it is specified that soils with 30% or less of their particles retained on the ¾" sieve can be utilized in this testing method.

Soils fitting this criterion are typically granular or fine-grained soils that will compact well under the exerted pressure and thus yield reliable maximum dry density results. The presence of too many larger particles could interfere with the compaction process and lead to inconsistent or non-representative results.

In contrast, soils with more than 30% of particles retained on the ¾" sieve are generally unsuitable because their larger particle size makes them less responsive to the compaction method used in the test. Additionally, compacted soils from a different method, or those with no restrictions on particle size, may not align with the goals of the Modified Proctor test, which seeks to standardize conditions for measurable outcomes.